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After the Shah was overthrown in 1979, the US cut economic and diplomatic ties.

The US passed further laws in 1996 restricting trade with the regime – these also seek to impose such conditions on non-US firms.

The EU traded with Iran until it stepped up its nuclear programme.

What about banks?

It was legal under US law for foreign banks to process dollar payments for Iranian businesses – under a strict regulatory code – until 2008.

What about Iran’s nuclear plans?

The UN Security Council imposed economic sanctions on all companies linked to the nuclear programme in 2010 as the country stepped up what the UN believes is a concerted effort to create a nuclear bomb.

Nuclear, oil and gas, and petrochemical trade is banned while banks and insurers are also barred from dealing with Iran by the UN.